A variety of techniques have been used for enhanced oil recovery (e.g., the recovery of hydrocarbons from oil containing reservoirs in which the hydrocarbons no longer flow by natural forces). Such techniques can include water injection and/or subsequent gas flooding, among others. Water injection can be useful to recover some hydrocarbons, however, only about a third of the hydrocarbons are recovered using this technique. As such, typically water injection procedures are followed by gas flooding procedures. Gas flooding can be performed with a miscible gas, which reduces the viscosity of oil present in the oil containing reservoir in order to increase the flow of hydrocarbons to a production well. Carbon dioxide, in a supercritical state, has been used as a miscible fluid to reduce the viscosity of the oil in the oil containing reservoirs. Supercritical carbon dioxide is one of the most effective and least expensive of the miscible fluids.
Gas flooding, however, can be accompanied with a number of drawbacks. One main problem encountered is poor sweep of the oil containing reservoir. Poor sweep occurs when the gas injected into the oil containing reservoir during a gas flooding process flows through the paths of least resistance due to the low viscosity of the gas, thus bypassing significant portions of the formation. When the gas bypasses significant portions of the formation, less oil is contacted with the gas, reducing the likelihood that the gas will reduce the viscosity of the oil producing poor sweep. In addition, due to the low density of the gas, the injected gas can rise to the top of the formation and “override” portions of the formation, leading to early breakthrough of the gas at the production well, leaving less gas within the oil containing reservoir to contact with the oil, again reducing the likelihood that the gas will reduce the viscosity of oil.
To enhance the gas flooding process effectiveness, it has been suggested that a surfactant be added to the supercritical carbon dioxide to generate an emulsion in the formation. An emulsion can generate an apparent viscosity of about 100 to about 1,000 times that of the injected gas, therefore, the emulsion can inhibit the flow of the gas into that portion of the oil containing reservoir that has previously been swept. In other words, the emulsion can serve to block the volumes of the oil containing reservoir through which the gas can short-cut, thereby reducing its tendency to channel through highly permeable fissures, cracks, or strata, and directing it toward previously unswept portions of the oil containing reservoir. As such, the emulsion can force the gas to drive the recoverable hydrocarbons from the less depleted portions of the reservoir toward the production well.